Curbing corrosion

December 2012 - The endless effort to make automobiles lighter receives plenty of attention nowadays, as OEM suppliers look for the next material—from aluminum to carbon fiber—to maximize fuel economy. Whether it’s metal or not, real material advancements are made when weight reduction begets higher strength.

SSAB, the Stockholm-based steelmaker with its U.S. head office in Lisle, Ill., recently introduced its next generation ultra-high-strength automotive steel, Docol 1400 MZE. It’s the European version of the Docol 1300M (as well as the 1500M), which is produced for U.S. automakers. With an electrogalvanized coating for corrosion protection, the Docol 1400 MZE’s inverse strength-to-weight formula gives it high crash-test ratings and hydrogen embrittlement resistance. The cold-rolled steel is heat treated in a continuous annealing line and offered in thicknesses of 0.51 millimeters to 2.10 millimeters in widths up to 1,527 millimeters.

As aluminum makes strides in panels, chassis and other components, so too does steel, according to Roger Lidgren, general manager, automotive at SSAB. Steel has been the material of choice for longer, and historically its manufacturing costs are lower. Even with new ultra-high-strength grades, steel can be manipulated with established techniques like welding, stamping and roll forming because of its clean composition.

“It’s easy to make high-strength steel,” says Lidgren. “You drive some carbon into it, quench it and you have really tough material. The more alloy elements you add, the greater the risk of cracking or having poor weldability. So our whole method of working is focused on adding as few alloys as possible to our steel and through our processing get to the properties that our customers demand. We try to keep it pure for consistent mechanical properties.”

The specific applications for 1400 MZE include cross members, rocker panels, A-pillars and more, depending on a manufacturer’s design. SSAB says it can be used for impact beams, sill reinforcements, bumpers, and hybrid or electric battery protection. The 1400 designation refers to the tensile strength in megapascals.

“When we have to provide OEMs, designers and tool manufacturers with what this material can and can not do, we find there are several possibilities for incorporating it in the design of products,” Lidgren adds.

To test its material in one instance, SSAB took the Docol 1400 MZE to Gestamp Metal Forming in Germany, according to a press release. Gestamp tested the 1400 MZE for a side impact beam usually made from cold-rolled 1200 megapascal steel. The 1400 MZE beam cut costs and weight without requiring changes to the production process in place for the 1200 beam.

That constant automotive development process, which began in the 1980s, is tailored to the demands of its customers. SSAB digests feedback from OEMs regarding their needs, and comes up with a new grade. When it finalizes a thinner gauge, stronger steel, SSAB tests the steel before it presents it to the OEMs.

“You need to have approval from the OEMs otherwise you can’t deliver one single pound,” Lidgren explains. “We test and test before taking it to market. We try to take away all the surprises. That’s our typical Swedish way of doing things.”

Beyond the car

SSAB, also known for its Hardox steel plate, sees uses beyond automotive parts. It could be incorporated into wear-resistant applications, like liners for the trucking industry. Manufacturers could form square or rectangular mechanical tubing used for four-wheel all-terrain vehicles, recreational vehicles or buses—“any vehicle that moves,” Lidgren says. “This material is so hard so it can compete with ultra-high-strength steel plate.”

The company also has worked with agricultural spray booms, where a manufacturer needed to extend a 90-foot boom by 20 feet. However, increasing the length rendered the boom too heavy to operate. “So again, you need to keep the weight constant,” Lidgren says, which at 110 feet required the ultra-high-strength steel. “The material is very useful.”

Ultimately, the automotive industry is what keeps SSAB pushing the envelope with thinner, lighter steel that’s stronger than the previous generation.

“This product and process development is constantly driving our company to higher and higher strength levels,” Lidgren says. “I believe steel, in the long term, will be the main material in car bodies.”MM